This invention relates to a skew detection system for use with the flaps, slats or other moveable control surfaces of an aircraft.
FIG. 1 illustrates diagrammatically the high lift leading edge control surfaces or slats 1 of an aircraft wing. Each slat 1 is typically driven between extended and retracted positions by means of a pair of rotary actuators, the actuators being positioned adjacent opposite ends of the slat. It will be appreciated that in the event that one of the actuators of one of the slats, or the drive arrangement associated therewith, fails whilst the other continues to operate, then the slat will become skewed relative to the wing. When one or more of the control surfaces of an aircraft become skewed, then the aerodynamics of the aircraft may be adversely affected. For example, in the event that the degree of skew of a slat becomes too great, then the angle of attack which can be maintained by the wing for a given airspeed without stalling will change, and remedial action may be required to permit control of the aircraft to compensate for the presence of the skew condition. Clearly, in order to permit appropriate remedial action to be taken it is desirable to be able to detect the presence of a skew condition before the degree of skew is such that control of the aircraft is impaired, and to provide a suitable warning signal to the pilot of the aircraft.
In the arrangement illustrated diagrammatically, in FIG. 1, the wing includes five slats 1, a first one of which is located inboard of a wing mounted engine, the remaining flour slats 1 being located outboard of engine. As mentioned before, each slat 1 is driven by a pair of actuators.
FIGS. 1 to 4 illustrate the slats 1 with one of the slats in a skewed condition. The position occupied by the skewed slat depends upon which of the two actuators associated with the slat has failed and upon whether the slats were being moved towards their extended positions or towards their retracted positions at the time at which the actuator failure occurred.
It is an object of the invention to provide a system whereby a skew condition can be detected, system being of a relatively simple and convenient form. Another object of the invention is to provide a skew detection system for use with a control surface system having a plurality of control surfaces located adjacent one another, and whereby a skew condition occurring with any of the surfaces can be detected using only two sensors.
According to an aspect of the present invention there is provided a skew detection system for use in sensing the occurrence of a skew condition in a system having a plurality of control surfaces located adjacent one another and which, in use, are driven to move simultaneously and at the same speed as one another, the skew detection system comprising a detector arrangement extending over and movable with the surfaces, between a first location on one of the surfaces and a second location on another of the surfaces, at least part of the detector arrangement being arranged to move in the event that one or more of the surfaces becomes skewed, and a sensor arranged to permit a change in the position of the said part of the detector arrangement to be detected.
The detector arrangement may comprise a plurality of elements arranged in end-to-end configuration. The elements may be provided with end surfaces having chamfered regions, the elements being arranged such that, in the event of a skew condition arising, the end surfaces of two adjacent elements slide over one another resulting in the chamfered regions of the adjacent end surfaces engaging one another, and consequently in the assembly of elements reducing in overall effective length. A compression spring may be provided to urge the elements into engagement with one another. The sensor may be positioned to monitor the position of an end one of the elements which moves when the overall effective length of the assembly changes.
Alternatively, the elements may be arranged to co-operate with one another by arrangements comprising a ball associated with one of the elements, the ball being received within a socket associated with another of the elements, the socket having a ramped side wall arranged such that, in the event of a skew condition arising, the ball rides over the ramped side wall, increasing the overall effective length of the assembly.
In another arrangement, the detector arrangement may comprise a cable extending continuously between the first and second locations and arranged such that, in the event of a skew condition occurring, the length of the cable between the first and second locations increases, the movement of a part of the cable past the sensor being monitored.
According to another aspect of the invention there is provided a skew detection system for use with a control surface system having a plurality of control surfaces located adjacent one another, the skew detection system comprising a first sensor operable to monitor the position of part of one of the surfaces, and a second sensor operable to monitor the position of part of another of the surfaces, the second sensor further being sensitive to the occurrence of a skew condition at locations between the said parts of the surfaces.
In use, where no skew condition occurs, then all of the control surfaces of the system will move substantially simultaneously, and the outputs of the first and second sensors will show that the associated parts of the surfaces have moved by the same distance. A difference in the sensed positions indicates that a skew condition has arisen, and appropriate control adjustments and warnings can be triggered.
Each sensor conveniently comprises a rotary position sensor arranged to be driven by movement of the associated surface. The position sensor may include a pinion arranged to be driven by a rack carried by the surface. The rack may comprise a chain.
The rack associated with the second sensor is preferably moveable relative to the associated control surface, such movement occurring in the event of the occurrence of a skew condition intermediate the parts of the surfaces with which the sensors are associated so that the second sensor is sensitive to the occurrence of such a skew condition.
An elongate flexible member is preferably provided, the member extending across all of the control surfaces with which the detection system is used, the member being guided adjacent the edges of each control surface, and being coupled to the rack associated with the second sensor to cause movement of the rack associated with the second sensor relative to the associated control surface in the event of a skew condition arising. The flexible member conveniently comprises a cable. The cable is conveniently guided by extending through tubular guide members located adjacent the edges of the control surfaces.
Alternatively, a plurality of members may be arranged in end-to-end configuration, the assembly of the members extending over the control surfaces the position of at least one of the members changing in the event of a skew condition, the rack being coupled to one of the members such that movement of the said member causes movement of the rack.
The skew detection system is suitable for use with a range of control surface systems, for example the slats of a high lift leading edge system or the trailing edge flaps of an aircraft wing.